View source for Krypton fluoride laser

[[File:Electra Laser System NRL 2013.png|thumb|alt=The electra laser at NRL is a KrF laser that demonstrated over 90,000 shots in 10 hours.|The electra laser at NRL is a KrF laser that demonstrated over 90,000 shots in 10 hours.]]
A '''krypton fluoride laser''' ('''KrF laser''') is a particular type of [[excimer laser]],<ref>Basting, D. and Marowsky,G., Eds., ''Excimer Laser Technology,'' Springer, 2005.</ref> which is sometimes (more correctly) called an exciplex laser. With its 248 nanometer wavelength, it is a deep ultraviolet laser which is commonly used in the production of semiconductor [[integrated circuit]]s, industrial micromachining, and scientific research. The term [[excimer]] is short for 'excited dimer', while exciplex is short for 'excited complex'. An excimer laser typically contains a mixture of: a noble gas  such as argon, krypton, or xenon; and a halogen gas such as fluorine or chlorine.  Under suitably intense conditions of electromagnetic stimulation and pressure, the mixture emits a beam of coherent stimulated radiation as [[laser light]] in the ultraviolet range.
KrF and ArF excimer lasers are widely incorporated into high-resolution [[photolithography]] machines, one of the critical tools required for [[microelectronic]] chip manufacturing in nanometer dimensions. Excimer laser lithography<ref name=ieee1982>{{cite journal|doi=10.1109/EDL.1982.25476|title=Ultrafast deep UV Lithography with excimer lasers|year=1982|last1=Jain|first1=K.|last2=Willson|first2=C.G.|last3=Lin|first3=B.J.|journal=IEEE Electron Device Letters|volume=3|issue=3|pages=53–55 |bibcode=1982IEDL....3...53J|s2cid=43335574 }}</ref><ref name=spie1990>Jain, K. "Excimer Laser Lithography", SPIE Press, Bellingham, WA, 1990.</ref> has enabled transistor feature sizes to shrink from [[800 nanometer]]s in 1990 to 10 nanometers in 2016.<ref name=spie2010>La Fontaine, B., [http://spie.org/x42152.xml "Lasers and Moore's Law"], SPIE Professional, Oct. 2010, p. 20.</ref><ref name=Samsung10nm>Samsung Starts Industry's First Mass Production of System-on-Chip with 10-Nanometer FinFET Technology; https://news.samsung.com/global/samsung-starts-industrys-first-mass-production-of-system-on-chip-with-10-nanometer-finfet-technology</ref>
==Theory==
A krypton fluoride laser absorbs energy from a source, causing the [[krypton]] gas to react with the [[fluorine]] gas producing the exciplex krypton fluoride, a temporary [[complex (chemistry)|complex]] in an excited energy state:
:2 Kr + {{chem|F|2}} → 2 KrF
The complex can undergo spontaneous or stimulated emission, reducing its energy state to a metastable, but highly [[repulsive state|repulsive ground state]]. The ground state complex quickly dissociates into unbound atoms:
:2 KrF → 2 Kr + {{chem|F|2}}
The result is an [[excimer laser|exciplex laser]] which radiates energy at 248&nbsp;nm, near the [[ultraviolet]] portion of the [[spectrum]], corresponding with the energy difference between the ground state and the excited state of the complex.
==Example Systems==
There have been several of these lasers built for ICF experiments; examples include:<ref>"Proceedings of the 4th international workshop on KrF laser technology" Annapolls Maryland, May 2, 1994 to May 5th 1994</ref>
* '''Los Alamos''' built a KrF laser in 1985 to prove test firing of beam with an energy level of 1.0 × 10<sup>4</sup> [[joule]]s.  This was part of the larger Aurora laser research effort that looked at {{CO2}} lasers and other systems.
* Nike Laser.  The Laser Plasma Branch of the [[Naval Research Laboratory]] completed a KrF laser called the [[Nike laser]] that can produce about 4.5 × 10<sup>3</sup> joules of UV energy output in a 4 [[nanosecond]] pulse.  The NIKE laser was switched to an [[Argon fluoride laser]] after 2013 to show the impact of going to shorter (193&nbsp;nm) wavelengths.
* '''[[Naval Research Laboratory]]''' built the Electra laser and Nike to prove out both KrF and ArF lasers for ICF approaches.  In 2013, Electra demonstrated 90,000 shots over 10 hours of operation.<ref name="Obenschain, Stephen 2015">Obenschain, Stephen, et al. "High-energy krypton fluoride lasers for inertial fusion." Applied optics 54.31 (2015): F103-F122.</ref>
* '''Rutherford Appleton Laboratory''' built the Sprite and Titania KrF lasers<ref>Divall, E. J., et al. "Titania—a 1020 W cm− 2 ultraviolet laser." Journal of modern optics 43.5 (1996): 1025-1033.</ref>
* '''Japan's Electrotechnical Laboratory''' built the Ashura and Super Ashura KrF lasers.<ref>Okuda, I., et al. "Performance of theSuper-ASHURA'main amplifier." [[Fusion engineering and design]] 44.1-4 (1999): 377-381.</ref>
* '''China Institute for Atomic Energy''' had a laser before the middle-1990's
* '''Livermore National Laboratory''' developed a KrF laser and amplifier known as a Raman Amplifier Pumped by Intensified Excimer Radiation (RAPIER) system.<ref>https://lasers.llnl.gov/multimedia/publications/pdfs/etr/1979_06.pdf {{Bare URL PDF|date=August 2024}}</ref>
==Applications==
This laser has also been used to produce soft X-ray emission from a [[plasma (physics)|plasma]], through irradiation by brief pulses of this laser light. Other important applications include manipulating of various materials such as plastic, glass, crystal, composite materials and living tissue. The light from this [[UV laser]] is strongly absorbed by [[lipid]]s, [[nucleic acid]]s and [[protein]]s, making it useful for applications in medical therapy and surgery.
===Microelectronics===
The most widespread industrial application of KrF excimer lasers has been in deep-ultraviolet [[photolithography]]<ref name= ieee1982 /><ref name=spie1990 /> for the manufacturing of [[microelectronic]] devices (i.e., semiconductor [[integrated circuit]]s or "chips"). From the early 1960s through the mid-1980s, Hg-Xe lamps had been used for lithography at 436, 405 and 365&nbsp;nm wavelengths. However, with the semiconductor industry's need for both finer resolution (for denser and faster chips) and higher production throughput (for lower costs), the lamp-based lithography tools were no longer able to meet the industry's requirements. This challenge was overcome when in a pioneering development in 1982, deep-UV excimer laser lithography was demonstrated at IBM by K. Jain.<ref name=ieee1982 /><ref name=spie1990 /><ref>Basting, D., et al., "Historical Review of Excimer Laser Development," in Excimer Laser Technology, D. Basting and G. Marowsky, Eds., Springer, 2005.</ref> With phenomenal advances made in equipment and technology in the last two decades, modern semiconductor electronic devices fabricated using excimer laser lithography now total more than $400 billion in annual production. As a result, it is the semiconductor industry view<ref name=spie2010 /> that excimer laser lithography (with both KrF and ArF lasers) has been a crucial factor in the predictive power of [[Moore's law]]. From an even broader scientific and technological perspective: since the invention of the laser in 1960, the development of excimer laser lithography has been highlighted as one of the major milestones in the 50-year history of the laser.<ref>[http://www.laserfest.org/lasers/history/timeline.cfm American Physical Society / Lasers / History / Timeline]</ref><ref>[http://spie.org/Documents/AboutSPIE/SPIE%20Laser%20Luminaries.pdf SPIE / Advancing the Laser / 50 Years and into the Future]</ref><ref>[http://www.stfc.ac.uk/Resources/PDF/Lasers50_final1.pdf U.K. Engineering & Physical Sciences Research Council / Lasers in Our Lives / 50 Years of Impact] {{webarchive|url=https://web.archive.org/web/20110913160302/http://www.stfc.ac.uk/Resources/PDF/Lasers50_final1.pdf |date=2011-09-13 }}</ref>
===Fusion Research===
The KrF laser has been used in [[nuclear fusion]] energy research since the 1980s. This laser offers several advantages:<ref name="Obenschain, Stephen 2015"/>
* High rate repetition shots - because the KrF is made using gas it does not heat up, allowing for higher shot rates.
* Higher beam uniformity
* Relatively shorter wavelength for improved ICF compression.
==Safety==
The light emitted by the KrF is invisible to the human eye, so additional safety precautions are necessary when working with this laser to avoid stray beams. Gloves are needed to protect the skin from the potentially [[carcinogen]]ic properties of the UV beam, and UV goggles are needed to protect the eyes.
==See also==
*[[Argon fluoride laser]]
*[[Nike laser]]
*[[Laser]]
*[[Krypton difluoride]]
*[[Krypton]]
*[[Fluorine]]
*[[Excimer laser]]
*[[Excimer lamp]]
*[[Photolithography]]
*[[Excimer]]
==References==
{{reflist}}
==External links==
*[https://web.archive.org/web/20070203205901/http://other.nrl.navy.mil/LaserFusionEnergy/lasercreation.htm Laser fusion energy]
*[https://web.archive.org/web/20110517215301/http://other.nrl.navy.mil/nike.html Nike KrF Laser Facility]
*[http://www.nikon-precision.com/products/nsr/krf/fs_krf.htm Nikon KrF] {{Webarchive|url=https://web.archive.org/web/20050907154032/http://www.nikon-precision.com/products/nsr/krf/fs_krf.htm |date=2005-09-07 }}
{{Excimer lasers}}
[[Category:Excimer lasers]]
[[Category:Krypton]]
[[Category:Fluorine]]